Motion in Radiotherapy Martijn Engelsman. 2 Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motion Motion

Motion in Radiotherapy

Martijn Engelsman

2

Contents

• What is motion ?

• Why is motion important ?

• Motion in practice

• Qualitative impact of motion

• Motion management

• Motion in charged particle therapy

3

What is motion ?

4

Motion in radiotherapy

• Aim of radiotherapy– Deliver maximum dose to tumor cells and

minimum dose to surrounding normal tissues

• “Motion”– Anything that may lead to a mismatch between

the intended and actual location of delivered radiation dose

5

Radiotherapy treatment process

1) Diagnosis

2) Patient immobilization

3) Imaging (CT-scan)

4) Target delineation

5) Treatment plan design

6) Treatment delivery (35 fractions)

7) Patient follow-up

6

Why is motion important ?

7

PTV concept (1)

GTV (Gross Tumor Volume): = 5 cm, V = 65 cm3

CTV (Clinical Target Volume): = 6 cm, V = 113 cm3

PTV (Planning Target Volume): = 8 cm, V = 268 cm3

High dose region

(ICRU 50 and 62)

8

PTV concept (2)

• Margin from GTV to CTV– Typically 5 mm or patient and tumor specific

– Improved by:• Better imaging

• Physician training

• Margin from CTV to PTV– Typically 5 to 10 mm

– Tumor location specific

– Improved by:• Motion management

• Smart treatment planning

GTVCTVPTVHigh Dose

9

Example source of motion

www.pi-medical.gr

35 Fractions=

35 times patient setup

10

Sources of motion

• Patient setup

• Patient breathing / coughing

• Patient heart-beat

• Patient discomfort

• Target delineation inaccuracies

• Non-representative CT-scan

• Target deformation / growth / shrinkage

• Etc., etc. etc.

11

Subdivision of motion

• Systematic versus Random

• Inter-fractional versus Intra-fractional

• Treatment Preparation versus Treatment Execution– Less commonly used

12

Systematic versus Random

• Systematic– Same error for all fractions (possibly even all patients).

• Random– Unpredictable. Day to day variations around a mean.

• Known but neither– Breathing, heartbeat

13

x

y

Setup errors for three patients

Beam’s Eye View

14

Systematic (x)

Random (y)

Random (x)

Setup errors for a single patient

Systematic (y)

15

Inter-fractional versus Intra-fractional

• Inter-fractional– Variation between fractions

• Intra-fractional– Variation within a fraction

16

Treatment preparation versus treatment execution


3) CT-scan




Treatment preparation

Treatment execution

Always systematic

Systematic and/or random

17

Motion in practice

18

Systematic Inter-fractional Treatment preparation

Random Intra-fractional Treatment execution

Target delineation

Steenbakkers et al.

Radiother Oncol. 2005; 77:182-90

19



Patient setup

x

y

20



Target deformation / motion 1/3

Target

Bladder

21




Target

Bladder

22


3) CT-scan





23

Breathing motion



Movie by John Wolfgang

“ ”

24

Qualitative impact of motion

25

Importance of motion

• Breathing motion / heart beat

• Systematic errors

• Random errors

Raise your hand to vote

Let’s “prove” it

Most

Least

Almost least

26

Simulation parameters (1)

GTVCTVPTVHigh Dose

GTVCTV

High Dose

To enhance the visible effect of motion: High dose conformed to CTV

27

GTVCTV

High Dose

Parallel opposed beamsDirection of motion

Simulation parameters (2)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 6050

60

70

80

90

10095 %

Do

se

(%

of

pre

sc

rib

ed

do

se

)

distance from beam axis (mm)

CTV

28

80 85 90 95 100 1050

5

10

15

20

25

30

35

Dose, % of ICRU reference dose

Vo

lum

e a

.u.

Amplitude of breathing motion:

0 mm

5 mm

10 mm

29

80 85 90 95 100 1050

5

10

15

20

25

30

35


Vo

lum

e a

.u.

Standard deviation of random errors:

0 mm

5 mm

10 mm

30

80 85 90 95 100 1050

5

10

15

20

25

30

35


Vo

lum

e a

.u.

Systematic error:

0 mm

5 mm

10 mm

310 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

Dose (Gy)

TC

P

DVH reduction into:

• Tumor Control Probability (TCP)

• Assumption: homogeneous irradiation of the CTV to 84 Gy results in a TCP = 50 %

32

Tumor motion and tumor control probability

Amplitude of breathing motion

(mm)

Random setup errors (1SD)

(mm)

Systematic setup error

(mm)TCP

(%)

0 0 0 47.3

5 - - 47.0

10 - - 46.3

15 - - 44.3

- 5 - 46.8

- 10 - 43.5

- 15 - 36.9

- - 5 45.5

- - 10 40.1

- - 15 6.0

Typical motion:

33

Importance of motion

• Breathing motion / heart beat

• Systematic errors

• Random errors

Therefore …

Most

Least

Almost least

34

Why are systematic errors worse ?

dose

CTV

Random errors / breathing blurs the cumulative dose distribution

Systematic errors shift the cumulative dose distribution

Slide byM. van Herk

35

• Systematic errors- Same part of the tumor always underdosed

• Random errors / Breathing motion / heart beat- Multiple parts of the tumor underdosed part of the time,

correctly dosed most of the time

But don’t forget: Breathing motion and heart beat can have systematic effects on target delineation

In other words…

36

Motion management

37



3) CT-scanning



6) Treatment delivery

38

Patient immobilization

Breast board

Intra-cranial mask

GTC frame

www.massgeneral.og

www.sinmed.com

www.sinmed.com

Leg pillow

39

Benefits of immobilization

• Reproducible patient setup

• Limits intra-fraction motion

40



3) CT-scanning




41

CT-scanning

• Multiple CT-scans prior to treatment planning- Reduces geometric miss compared to single CT-scan

• 4D-CT scanning- Extent of breathing motion- Determine representative tumor position

• See lecture “Advances in imaging for therapy”

42



3) CT-scanning




43

Target delineation

• Multi-modality imaging

- CT-scan, MRI, PET, etc.

• Physician training and inter-collegial verification

• Improved drawing tools and auto-delineation

44



3) CT-scanning




45

Treatment plan design

• Choice of beam angles

- e.g. parallel to target motion

• Smart treatment planning

• Robust optimization

• IMRT

• See, e.g., lecture “Optimization with motion and uncertainties”

46



3) CT-scanning




47

Magnitude of motion in treatment delivery

• Systematic setup error– Laser: = 3 mm

– Bony anatomy: = 2 mm

– Cone-beam CT: = 1 mm

• Random setup errors– = 3 mm

• Breathing motion– Up to 30 mm peak-to-peak

– Typically 10 mm peak-to-peak

• Tumor delineation– See next slide

48

Tumor delineation

• 22 Patients with lung cancer

• 11 Radiation oncologists from 5 institutions

• Comparison to median target surface

Rad. Onc. # Mean volume

(cm3)

Mean distance

(mm)

Overall SD

(mm)

1 36 -6.4 15.1

2 48 -3.7 11.6

3 53 -4.3 13.9

4 55 -2.4 7.0

5 58 -3.3 12.7

6 67 -1.6 10.0

7 69 -1.2 6.2

8 72 -1.0 6.6

9 76 -0.2 7.4

10 93 0.9 5.7

11 129 0.4 6.1

All 69 ( 25) -1.7 10.2

Steenbakkers et al.

Radiother Oncol. 2005; 77:182-90

5?

49

Motion management

50

Motion management for setup errors

• Portal imaging

51

Portal imaging

Obtained from Treatment Planning System

Obtained in treatment room

52

Setup protocol

• NAL-protocol (No Action Level)– Portal imaging for first Nm fractions

– Calculate a single correction vector compared to markers for laser setup

Lasers only

de Boer HC, Heijmen BJ.

Int J Radiat Oncol Biol Phys.

2001;50(5):1350-65

53

Motion management for breathing

• In treatment plan design- Margin increase- Overcompensating dose to margin- Robust treatment planning- See, e.g., lecture “Optimization with motion and

uncertainties”

• Control patient breathing- Breath-hold- Gated radiotherapy

54

Breathing traces

Trace PDF =ProbabilityDensityFunction

1)

2)

3)

55

Margin increase

56

Effect of blurring on dose profile (conformal)

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0Conformal beam

Unblurred Breathing Random setup errors Both

distance (from central axis, mm)

Do

se (

rela

tive

)Only a limited shift in 95% isodose level

57

Margin for breathing (conformal)

5 10 15

58

Margin for breathing (IMRT)

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0

IMRT beam


Do

se (

rela

tive

)

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0Conformal beam

Unblurred Breathing Random setup errors Both


Do

se (

rela

tive

)

HypotheticallySharpDose

Distribution

59

Margin for breathing (IMRT)

5 10 15

IMRT

60

Breath hold

61

Control / stop patient breathing

• Exhale position most reproducible

• Inhale position most beneficial for sparing lung tissue

62

Breath hold techniques

• Voluntary breath hold• Rosenzweig KE et al. The deep inspiration breath-hold technique in the treatment of

inoperable non-small-cell lung cancer. Int J Radiat Oncol Biol Phys. 2000;48:81-7

• Active Breathing Control (ABC)• Wong JW et al. The use of active breathing control (ABC) to reduce margin for breathing

motion. Int J Radiat Oncol Biol Phys. 1999;44:911-9

• Abdominal press– Negoro Y et al. The effectiveness of an immobilization device in conformal radiotherapy for

lung tumor: reduction of respiratory tumor movement and evaluation of the daily setup accuracy. Int J Radiat Oncol Biol Phys. 2001;50:889-98

63

Gating

64

Gated radiotherapy

• External or internal markers• Usually 20% duty cycle• Some residual motion

Gating window

65

Gating benefits and drawbacks

• Less straining for patient than breath-hold• Increased treatment time

• Internal markers– Direct visualization of tumor (surroundings)– Invasive procedure / side effects of surgery

• External markers– Limited burden for patient– Doubtful correlation between marker and tumor

position• Intra-fractional• Inter-fractional

+

+

+

-

-

-

66

Motion in charged particle therapy

67

T. Bortfeld

68

Range sensitivity

Paralell opposed -photons

Single field -protons

Single field -photons

Spherical tumor in lung

Displayed isodose levels: 50%, 80%, 95% and 100%

69





Range sensitivity


70





Range sensitivity


71

Dose-Volume Histogram (protons)

PTV (static)CTVGTVCTV-GTV

72

SOBP Modulation

Aperture

High-DensityStructure

BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

73

+ =

Passive scattering system

Aperture Range Compensator

Lateral conformation

Distal conformation

74

Smearing the range compensator

Aperture


BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

75

Smearing the range compensator

Aperture


BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

76

Smear

Setup

Error

A 0 0

B 0 10

C 10 0

D 10 10

A B C D

E F G HC D


77

Motion management in particle therapy

• Passive scattered particle therapy

• For setup errors and (possibly) breathing motion

- Lateral expansion of apertures

- Smearing of range compensators

• IMPT

- See, e.g., lecture “Optimization with motion and uncertainties”

78

Thank you for your attention

Documents

Motion in Radiotherapy Martijn Engelsman. 2 Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motion Motion